This invention relates to mobile, offshore, jack-up, marine platforms of the type used to explore for and produce oil and natural gas from locations under the sea, and particularly from locations under substantial depth of sea water, such as depths of about six hundred feet. Such locations may have sloping sea floor which would cause unacceptable tilting out of vertical of a platform mounted on a central column which is connected to a mat positioned on the sea floor. Such platforms need to be adjustable for sloping sea floor, with a central column rigidly cross-braced to withstand wind and wave action upon the long central column. The apparatus of this invention satisfies the aforementioned needs.